Qusay H. Mahmoud's Blog

Networking MIDlets and blocking operations

I get many email about the application featured in the article MIDP Database Programming with RMS. The application locks up the screen as the MIDlet tries to establish a wireless connection. This article was developed back in 2000 and back then everything worked perfectly. However, when developing networking MIDlets, pay special attention to blocking operations (e.g. methods that establish a connection to the network) which can lock up the screen, leaving the user frustrated with the application. To prevent this, all blocking operations should be performed in a separate thread. A more detailed explanation of this can be found in Preventing Screen Lockups of Blocking Operations in which I provide a detailed example of a network time MIDlet client.

To fix the problem in the Stock Quotes MIDlet from the MIDP Database Programming article, edit the QuotesMIDlet.java file, and:

1. Create a new method as follows:

   public void makeConnection() {
      try {
         String userInput = input.getString();
         String pr = getQuote(userInput);
         db.addNewStock(pr);
         ticker.setString(tickerString());
      } catch(IOException e) {
      } catch(NumberFormatException nfe) {
      }
      mainMenu();
   }
   

2. Replace the following piece of code:

   } else if (label.equals("Save")) {
      if(currentMenu.equals("Add")) {
         // add it to database
         try {
            String userInput = input.getString();
            String pr = getQuote(userInput);
            db.addNewStock(pr);
            ticker.setString(tickerString()); 
         } catch(IOException e) {
         } catch(NumberFormatException se) {
         }
         mainMenu();
      } 
   }
   

   with:

   } else if (label.equals("Save")) {
      if(currentMenu.equals("Add")) {
         Thread t = new Thread() {
            public void run() {
               makeConnection();
            }
         };
         t.start();
      }
   }
   

And this should solve the screen lockup problem. :-)

There will be lots of Java ME cool stuff at JavaOne this year. To get an idea of what's planned for then, take a look at Terrence Barr's Java ME Guide to JavaOne 2007. Q.

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